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Engine Cooling and Cabin Heating System Tutorial
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beetleman217
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PostPosted: Mon Jan 02, 2012 2:14 am    Post subject: Re: Engine Cooling and Cabin Heating System Tutorial Reply with quote

Paul Windisch wrote:
Many people don't know that the heat exchanger is operating all the time when the engine is running, regardless of the position of the heat control lever in the car. The lever in the car controls a diverter valve internal to the heat exchanger (another flap) via a cable that runs from the lever to the arm on the side of the heat exchanger. This valve directs air flow into the hose that leads to the heater channel when the heat is "on". When the heat is off, the valve closes the port that enters the car and opens a port on the top of the exchanger, toward the front. With the heat off, the fresh air tubes still deliver air to the exchanger to transfer excess heat from the cylinder head. This heat is then expelled through the top port on the exchanger and exits below the engine compartment. For this reason, even I you don't care to use the heater, if you still have heat exchangers, you should always have the fresh air tubes connected.


I have the exchangers off the car and after carefully studying them I can only see one port that is being opened and closed by the lever - the port to allow/shut off air to the cabin. So if there were single port exchangers such as mine, where would the hot air go when cabin heat is off?
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Paul Windisch
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PostPosted: Mon Jan 02, 2012 11:28 am    Post subject: Reply with quote

There is a vent on top of the exchanger, it is sort of round in shape. When the heat to the cabin is closed off, the hot air escapes through the vent.

In this picture, you can see the vent, it is what the spring is stretching across.

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beetleman217
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PostPosted: Wed Jan 04, 2012 8:06 am    Post subject: Reply with quote

Paul Windisch wrote:
There is a vent on top of the exchanger, it is sort of round in shape. When the heat to the cabin is closed off, the hot air escapes through the vent.


Here is my exchanger. I don't see any vent.
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Paul Windisch
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PostPosted: Wed Jan 04, 2012 9:41 am    Post subject: Reply with quote

Here, I cicled it and drew an arrow where the vent exhausts:

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beetleman217
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PostPosted: Thu Jan 05, 2012 2:45 am    Post subject: Reply with quote

I looked closely and finally got it. The dome actually has an opening at the bottom - the bottom is not welded to the HE like the rest of it. And it's hard to see but I guess when the flap is opened it actually lays flat on the inside if the dome shutting it off.
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bugninva
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PostPosted: Thu Jan 05, 2012 6:23 pm    Post subject: Reply with quote

beetleman217 wrote:
I looked closely and finally got it. The dome actually has an opening at the bottom - the bottom is not welded to the HE like the rest of it. And it's hard to see but I guess when the flap is opened it actually lays flat on the inside if the dome shutting it off.


yep, now you got it...
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Antonio Trejo Premium Member
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PostPosted: Fri Jan 06, 2012 1:22 pm    Post subject: Reply with quote

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I didn't know about that vent, thanks Paul! I got some photos about.
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PostPosted: Fri Jan 06, 2012 8:38 pm    Post subject: Reply with quote

Antonio Trejo wrote:
I didn't know about that vent, thanks Paul! I got some photos about.



that vent is precisely why the freshair hoses need to be connected to the heat exchangers *always*... lots of folks *think*(keyword) that in the summer they will disconnect and plug the freshair outlets to "help" cool the engine..... all they are doing is giving the heatexchangers a chance to overheat and transmit heat back into the heads and exhaust ports.... the vents prevent that....
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Breck
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PostPosted: Fri Jan 06, 2012 11:11 pm    Post subject: Reply with quote

Fantastic informative post. As some what of a newbe I have a 73 SB and a 64 bug, I am in the middle of a rebuild on the 64 and I do not see any of the baffle linkage on the back on my fan shroud. Is this correct or has it been removed by a previous owner. The bug has the original 1200 40hp motor. I also do not see any thermostats on the under side of the motor. This is a Cali bug(hot climate). If it has been removed, linkage and all. Why??? What would the purpose be in removing it?? I am just curious as to why one would make the cooling/heating system weaker. Breck
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Paul Windisch
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PostPosted: Sat Jan 07, 2012 6:17 am    Post subject: Reply with quote

I am not 100% familiar with the earlier cooling systems, but I know they are different. They didn't have flaps like the later cars, they used a thermostat that controlled a venturi ring at the fan inlet I believe. You might want to check in the 58-67 forum for more details about it.
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qwerty8669
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PostPosted: Sat Jan 07, 2012 10:39 am    Post subject: baja heat Reply with quote

I bought a baja recently and want to use it as a daily driver

I have a 68 baja I get decent heat ( not as good as what most of you guys are getting ) from the shop vac hoses the guy put in it. Her filled the factory inlets with great stuff and ran the hoses through where the back seat once was....

Have no rear deck lid just enough of it is there to hold the licesnse plate.....

Gonna have to get thermostat and fins to go with them.......don't believe I have either.

I get an exhaust smell in the cabin. It was stated that this happens with bajas without a deck lid.....I have the curved exhaust that exits close to the motor.....can I change the exit.point to keep the smell out of the cabin? Some of the exhaust has rust and could be getting the smell.from there also so gonna look into replacing that

Can I tell if I have the "good" heat exchangers without tearing them open?

Can I reseal them.....have read they leak sometimes since they are just clampshells.


here is photo

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torsionbar
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PostPosted: Fri Feb 10, 2012 4:42 pm    Post subject: Reply with quote

if you can't figure out all this cabin heat stuff, here's an idea:

http://boingboing.net/2012/02/10/extreme-diy-car-mods-volvo-wi.html

Laughing
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[air cooled vw's] are no longer suitable for the general public. The owner has to be be able to maintain the car. And that is after fixing all the deferred maintenance items and ill-conceived modifications. If you can't do those things you are pretty much screwed.
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flyboat
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PostPosted: Fri Feb 10, 2012 4:48 pm    Post subject: Reply with quote

torsionbar wrote:
if you can't figure out all this cabin heat stuff, here's an idea:

http://boingboing.net/2012/02/10/extreme-diy-car-mods-volvo-wi.html

Laughing

OMG, that is over the top. That would make the Redneck's top ten list. If he could hook a boiler to it, he'd have steam power. Hmmm!

I bet the stove pipe looks trendy coming through the roof.
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Paul Windisch
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PostPosted: Sun Feb 12, 2012 1:11 pm    Post subject: Reply with quote

I finally got some pics of defroster parts! Here they are:

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Once the heat travels through the large tube that comes up from the "Black Hole", that tube connects to the splitters (bottom right and left in the pic). If you look closely at the splitter, two of the outlets are larger than the center outlet. The center outlet goes to the center dash vent (upper middle in pic). One of the larger outlets goes to the corner of the windshield, the other goes to the smaller inlet on the dash vent duct (upper right and left in pic). The large inlet on the right and left dash ducts gets plumbed to the fresh air box. Here are some more pics:

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This is the splitter. It sits about 1/4 - 1/2 way down the black hole. Pay attention, you will see a metal strap; The tubing needs to be tucked into that strap properly, otherwise the hood hinge can crush the tube and block your defroster flow.

And here is a pic of the whole thing put together:

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beetleman217
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PostPosted: Tue Feb 21, 2012 7:37 am    Post subject: Reply with quote

This thread got me wanting to restore the thermostat mechanism on my car. Just as I was about to purchase all the bits, I consulted with members of a local beetle forum, explaining all the advantages that the system brings, and that if it fails, the spring opens the flaps thus saving the engine from frying.

However, a fellow replied that his mechanism had failed with the flaps closed - the thermostat siezed in the compressed position, and the engine fried. So it can happen. Did the German engineers not think about everything afterall? That got me thinking the whole thing over...

What do you say?
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Paul Windisch
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PostPosted: Tue Feb 21, 2012 11:12 am    Post subject: Reply with quote

A thermostat like this won't fail closed:

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He either had one of these thermostats (which CAN fail closed)

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Or, some other part of the system has failed, for example, the flaps rusted in position, or the thermostat was not properly adjusted, or the spring wasn't in place.

OEM thermostats (like the one shown in the top picture) are held under a partial vacuum to keep them compressed when at ambient temperature. When they are heated, the solution inside expands forcing the bellows to expand. The only way for them to fail is to have a breach of vacuum seal, which allows the bellows to decompress, which allows the spring on the flap rod to pull the flaps open. The thermostat won't fail closed, but that doesn't mean some other part of the system hasn't failed somehow. The "Fail Safe" of the thermostat assumes the rest of the system works properly.
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PostPosted: Tue Feb 21, 2012 4:00 pm    Post subject: Reply with quote

Paul, it is rare but the bellows type thermostats have failed closed. I had one on a parts engine that was fully compressed, but dead. I kept it for years before tossing it, I should have kept it because I'm on of the lucky few to have had one!
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PostPosted: Wed Feb 22, 2012 6:07 am    Post subject: Reply with quote

bugninva wrote:
Paul, it is rare but the bellows type thermostats have failed closed. I had one on a parts engine that was fully compressed, but dead. I kept it for years before tossing it, I should have kept it because I'm on of the lucky few to have had one!


Hmm, interesting. I would love to know how it failed that way...Think

Not doubting you, I'm genuinely curious.
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PostPosted: Wed Feb 22, 2012 4:42 pm    Post subject: Reply with quote

Crud or corrosion on the thermostat itself or the linkages kept it from opening???
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PostPosted: Thu Feb 23, 2012 1:09 am    Post subject: Reply with quote

So what you guys are saying is that even though there's a small chance of the thermo failing closed and frying the engine, the advantages it brings are worth taking the chance?

You would run your engine with the thermo and never worry about it?
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